Parse exists expressions

sqlparser/lib/src/analysis/types/resolver.dart

@@ -78,7 +78,10 @@ class TypeResolver {
         return resolveColumn(expr.resolved as Column);
       } else if (expr is FunctionExpression) {
         return resolveFunctionCall(expr);
-      } else if (expr is IsExpression) {
+      } else if (expr is IsExpression ||
+          expr is StringComparisonExpression ||
+          expr is BetweenExpression ||
+          expr is ExistsExpression) {
         return const ResolveResult(ResolvedType.bool());
       } else if (expr is BinaryExpression) {
         final operator = expr.operator.type;
@@ -89,10 +92,6 @@ class TypeResolver {
               [BasicType.int, BasicType.real, BasicType.text, BasicType.blob]);
           return ResolveResult(type);
         }
-      } else if (expr is StringComparisonExpression) {
-        return const ResolveResult(ResolvedType.bool());
-      } else if (expr is BetweenExpression) {
-        return const ResolveResult(ResolvedType.bool());
       } else if (expr is CaseExpression) {
         return resolveExpression(expr.whens.first.then);
       } else if (expr is SubQuery) {

sqlparser/lib/src/ast/ast.dart

@@ -145,6 +145,7 @@ abstract class AstVisitor<T> {
   T visitReference(Reference e);
   T visitFunction(FunctionExpression e);
   T visitSubQuery(SubQuery e);
+  T visitExists(ExistsExpression e);
   T visitCaseExpression(CaseExpression e);
   T visitWhen(WhenComponent e);
 
@@ -181,6 +182,9 @@ class RecursiveVisitor<T> extends AstVisitor<T> {
   @override
   T visitSubQuery(SubQuery e) => visitChildren(e);
 
+  @override
+  T visitExists(ExistsExpression e) => visitChildren(e);
+
   @override
   T visitSetComponent(SetComponent e) => visitChildren(e);
 

sqlparser/lib/src/ast/expressions/subquery.dart

@@ -16,3 +16,18 @@ class SubQuery extends Expression {
   @override
   bool contentEquals(SubQuery other) => true;
 }
+
+class ExistsExpression extends Expression {
+  final SelectStatement select;
+
+  ExistsExpression({@required this.select});
+
+  @override
+  T accept<T>(AstVisitor<T> visitor) => visitor.visitExists(this);
+
+  @override
+  Iterable<AstNode> get childNodes => [select];
+
+  @override
+  bool contentEquals(ExistsExpression other) => true;
+}

sqlparser/lib/src/ast/statements/select.dart

@@ -33,9 +33,9 @@ class SelectStatement extends Statement with ResultSet {
   @override
   Iterable<AstNode> get childNodes {
     return [
-      if (where != null) where,
       ...columns,
       if (from != null) ...from,
+      if (where != null) where,
       if (groupBy != null) groupBy,
       if (limit != null) limit,
       if (orderBy != null) orderBy,

sqlparser/lib/src/reader/parser/parser.dart

@@ -612,6 +612,13 @@ class Parser {
       final operator = _previous;
       final expression = _unary();
       return UnaryExpression(operator, expression);
+    } else if (_matchOne(TokenType.exists)) {
+      _consume(
+          TokenType.leftParen, 'Expected opening parenthesis after EXISTS');
+      final selectStmt = select();
+      _consume(TokenType.rightParen,
+          'Expected closing paranthesis to finish EXISTS expression');
+      return ExistsExpression(select: selectStmt);
     }
 
     return _postfix();

sqlparser/lib/src/reader/tokenizer/token.dart

@@ -35,6 +35,7 @@ enum TokenType {
   or,
   tilde,
   between,
+  exists,
 
   questionMark,
   colon,
@@ -104,6 +105,7 @@ const Map<String, TokenType> keywords = {
   'ALL': TokenType.all,
   'AND': TokenType.and,
   'OR': TokenType.or,
+  'EXISTS': TokenType.exists,
   'BETWEEN': TokenType.between,
   'DELETE': TokenType.delete,
   'FROM': TokenType.from,

sqlparser/test/parser/expression_test.dart

@@ -72,6 +72,17 @@ final Map<String, Expression> _testCases = {
     right: StringLiteral.from(token(TokenType.stringLiteral), '%A%\$'),
     escape: StringLiteral.from(token(TokenType.stringLiteral), '\$'),
   ),
+  'NOT EXISTS (SELECT * FROM demo)': UnaryExpression(
+    token(TokenType.not),
+    ExistsExpression(
+      select: SelectStatement(
+        columns: [StarResultColumn(null)],
+        from: [
+          TableReference('demo', null),
+        ],
+      ),
+    ),
+  ),
 };
 
 void main() {